There exists a major need for infrared imaging arrays in a variety of applications. For example, NASA Earth and space science applications need detector arrays for infrared imaging spectrometers.
Considerable effort has been expended to develop II-VI semiconductors, e.g., (Hg,Cd)Te, to achieve intrinsic semiconductor detectors capable of operating in the near and long wavelength infrared region of 3 to 30 micrometers. The fabrication of detectors in this range from III-V materials would be highly advantageous, because these materials are more highly developed and have properties that are superior to II-VI compounds.
Recently, quantum well detectors have been demonstrated in III-V materials. These detectors evidence good detectivity in the wavelength region near 10 micrometers. These are based on the process of infrared absorption between the ground and first excited states of the quantum wells. This approach is limited to a narrow range of wavelengths for a given detector, and is difficult to fabricate into large arrays because of the large number of multiple quantum wells (at least about fifty) required to obtain good optical absorption. They also exhibit complicated current-voltage characteristics because of the presence of high field domains required to maintain current continuity through the multiple quantum well structures.
Despite such advances, the need still exists for infrared detectors which provide good sensitivity, tunable over a wide range of wavelengths, and which can be fabricated into imaging arrays with good yields and high reliability.